In such toothed chains, use is made of different link plate types, since the toothed chain must be guided transversely with respect to its direction of circulation. For this purpose, the chain has integrated into it so-called guide link plates or cover link plates which, in the case of externally-guided toothed chains, are provided with a run-in web which projects laterally beyond the sprocket which interacts with the toothed chain.
With such guide link plates, it must be ensured that the rigidity of the guide link plate does not differ significantly from the rigidity of the toothed link plates situated at the inside. Specifically, if there is a significant difference here, then the guide link plates or cover link plates absorb higher tensile stresses and therefore cause higher stresses at the stress-critical regions, specifically in the contact region between the cover link plate and the cradle pieces pressed into the cradle piece openings, such that there is the risk of crack formation proceeding from these then overloaded regions. To eliminate said problem, known guide link plates have an opening in the region between the upper and lower link plate webs. Said opening serves to reduce the rigidity of the cover link plate.
For said guide link plates, a plurality of embodiments has already been disclosed in the prior art. For example, U.S. Pat. No. 5,345,753 has disclosed a guide link plate which, in the region between the upper and lower link plate webs, has an opening composed of a plurality of interconnected convex or concave curve segments. In said known cover link plate, the upper link plate web has a greater width than the lower link plate web, resulting in a non-uniform tensile force distribution; the upper link plate web absorbs a significantly greater tensile force than the lower link plate web.
Furthermore, the configuration of the opening with a plurality of concave or convex curve segments has the result that said opening can be produced only with difficulty. Such cover link plates are usually produced by means of a punching tool; on account of the complex configuration of the opening, bending of the edge regions of the opening and/or distortion of the link plates occurs as the inner opening is punched out.
A similar problem is also encountered with the cover link plate known from U.S. Pat. No. 6,171,209, which has a bone-shaped opening and which can likewise be produced only with difficulty on account of the alternating convex and concave curve segments.
Finally, U.S. Pat. No. 5,176,586 has disclosed a cover link plate whose opening between the cradle piece openings has an elongate oval configuration and in which the upper link plate web is formed so as to be significantly wider than the lower link plate web, that is to say there is again a non-uniform tensile force distribution with the result that the stress-critical points of the cradle piece openings are again subjected to non-uniform loading, and there is the risk of cracks forming proceeding from the contact zone between the cradle piece and the cradle piece opening.
The known cover link plates thus have the problem that, on account of their rigidity, they lead to non-uniform stress distributions in the toothed chain.